The purpose of this project was to evaluate the importance of phycoerythrin-containing phytoplankton, in particular coccoid cyanobacteria, to remote sensing. We proposed to estimate cyanobacteria abundance and pigmentation and their relationship to water-column optics. We have estimated the contribution of cyanobacteria to scattering and backscattering in both open ocean (Sargasso Sea) and coastal waters (western coast of North Atlantic and the California Current). Sampling and data processing is performed. Relationship between water column optics and phycoerythrin concentration and algorithms development are being carried out.